In a known manner, an ad hoc network is provided with no fixed infrastructure and stations, equipped with radio transmission and/or reception means and appropriate protocols make up the nodes of the network and communicate with each other by means of a radio channel, or several radio channels, which are shared.
Ad hoc networks are in particular used to implement tactical communications between military teams, moving over combat zones. For example, each team is equipped with a radio transceiver station that constitutes one node of an ad hoc network. Several teams are generally grouped together into groups, the teams within a same group for example falling under a same hierarchical commander. Groups may also be made up of military forces from different countries.
Certain groups may use communication protocols specific to them. In this way, heterogeneous ad hoc communication networks may be deployed over a same zone, and may not communicate with each other.
Each group generally constitutes an ad hoc network, or ad hoc sub-network, for ad hoc transmission dedicated to that group.
Distinct radio communication resources are allocated to each of these networks or sub-networks, for example at least one radio channel or predetermined time slot of such a channel.
Below, the term “network” will refer to one such network or sub-network.
Such situations of allied teams using heterogeneous transmission networks are also encountered in the technical migration phases of the radio communication means.
In such an environment, friendly fire may be avoided by the knowledge, at the nodes of a network dedicated to a team, of the geographical location of the allied teams, by implementing a data broadcast service indicating the position of each node in its geographical vicinity. This service is called “Blue Force Tracking” (BFT). The position of a node is for example provided by a position detection module whereof the node is typically equipped with a GPS (Global Positioning System) module.
The BFT service must be made available over all of the networks and sub-networks in a same geographical area, i.e. such a position message must be received by the nodes in a geographical neighborhood of the transmitting node, whether they are part of the same network as that transmitting node or another network.
Traditionally, any message or packet that must be broadcast from one network to another is done via at least one inter-network node. In the case of a BFT message, such processing also applies, since the current state of the art does not use geographical information to filter the broadcast. Thus, the positions of the nodes of a network are transmitted from one network to all of the nodes of another network by means of at least one specific node, called gateway node. This generates a significant burden on the radio networks, in particular their ad hoc networks, since each position update for a node gives rise to a message that must be communicated to all of the nodes of the other network, by means of the gateway node(s), in the absence of filtering.